1. Field of the Invention
This invention relates to a semiconductor device and a method for manufacturing the same.
2. Description of the Prior Art
In the past, one conductivity type diffusion layer in a semiconductor substrate and a reverse conductivity type semiconductor wiring layer have been connected with a film of a metal such as aluminum or the like, in order to achieve ohmic contacts without forming any PN junction.
Now, a method for manufacturing the semiconductor device, wherein a P type diffusion layer formed on an N-type silicon substrate is connected with an N-type polycrystalline silicon wiring, will be described with reference to FIGS. 1 (a) to 1 (d).
First, as shown in FIG. 1 (a), a silicon oxide film 2 of about 20 nm thickness is formed on an N-type silicon substrate 1 and an N-type polycrystalline silicon wiring layer 3 of about 400 nm thickness is formed on the silicon oxide film 2, which is followed by being processed to patterning for forming wirings with a photolithographic technology. Then, the silicon oxide film 2 is removed to partially expose the silicon substrate. Thereafter, a silicon oxide film 4 is formed on the total surface of a silicon wafer and then, after ion implantation of boron on the surface of the N-type silicon substrate 1, a P-type diffusion layer 5 is formed by performing an annealing step. The boron ions are implanted in the direction of arrows as shown in FIG. 1 (a).
Then, as shown in FIG. 1 (b), the silicon oxide film 4, which covers a contact portion 6 on the surface of the P-type diffusion layer 5 and an adjacent connection portion 7 on the N-type polycrystalline silicon 3, is selectively removed to form an aperture portion 8.
Thereafter, as shown in FIG. 1 (c), an aluminum film 10 of about 600 nm thickness is formed on the total surface of the wafer.
Finally as shown in FIG. 1 (d), the aluminum film 10, except the film formed on the aperture portion 8 and the silicon oxide film 4 of the peripherally thereof, is subjected to a patterning process due to etching to form an aluminum connection wiring layer 10a which connects the contact portion 6 on the P-type diffusion layer 5 with the connection portion 7 on the N-type polycrystal silicon wiring layer 3.
In this case, the coverage length D of the aluminum connection wiring layer 10a on the silicon oxide film 4 is about 0.6 .mu.m.
In the prior art semiconductor device and the method for manufacturing the same, as mentioned above, aluminum 10 is used to connect the diffusion layer with the semiconductor wiring and thus it is necessary to perform an alignment of aluminum 10a with the contact portion 6 and the connection portion 7 and then to perform an etching process. Therefore, there is a drawback that the manufacturing process becomes longer. In addition, there is another drawback that it is difficult to attain a high integration density due to the wide alignment margin.
In addition, formation of an inter-wiring insulating film which is formed to make additional wiring thereon is restricted to be only subjected to a heat treatment not higher than about 400.degree. C. because the connection wiring 10a is composed of aluminum. Thus, there is an additional drawback that the freedom of the manufacturing is limited, causing a poor evenness of the wafer surface.